Occam's Razor.

In Philosophy, Occam's Razor is the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements.

Attributed to William of Ockham, a 14th-century English philosopher and theologian, it is frequently cited and translated as:

'Entities must not be multiplied beyond necessity'.

... although Occam never used these exact words. Popularly, the principle is sometimes paraphrased as:

'Of competing theories, the simplest is to be preferred'.

Also, this philosophical razor advocates that when presented with competing theories, one should prefer the theory that requires the fewest assumptions.

So, in practice, when we have a set of competing theories, we should first select theories with least assumptions, then choose the simplest one from them.


Sources:
- Occam's Razor on Wikipedia,
- my own thinking.